The measurement of external works is a critical aspect of architectural quantity surveying and project management in Kenya. External works include all construction activities outside the main building structure, which significantly affect the overall project cost and quality. Accurate documentation and measurement of these elements ensure proper budgeting, scheduling, and execution. This chapter focuses on key external works elements such as landscaping, rendering, and drainage, providing detailed principles for their measurement and documentation within the architectural profession.

3.1 External Works Elements Documentation

External works encompass various site development and finishing activities that contribute to the functionality and aesthetics of a building project. Proper documentation of these elements is essential for clear communication among architects, contractors, and quantity surveyors. In Kenya, external works often involve site-specific considerations such as soil conditions, climate, and local materials, which must be reflected accurately in measurement practices.

3.1.1 Landscaping works

Landscaping works integrate natural and constructed elements to enhance the external environment of a building. They include soft landscaping, such as grass, trees and flower beds, and hard landscaping, such as parking areas, kerbs, paved walkways and cabro surfaces. Accurate documentation of landscaping is crucial for cost control and ensuring the design intent is realized, especially in public institutions such as county government offices or private developments like hotels.

3.1.1.1 Vehicular parking

Vehicular parking is the paved area set aside for cars and other vehicles to park and manoeuvre, made up of parking bays, access aisles, kerbs, drainage and markings. It must be documented with its layout, the number and size of bays, the pavement layers and the drainage, because these govern cost, usability and durability. A typical car bay is about 2.5 m wide by 5.0 m long, with a two-way aisle of about 6.0 m for right-angle parking, and accessible bays are made wider, about 3.6 m. Example: the parking for a new bank branch is documented on a site plan showing 24 bays, one accessible bay, the access aisle, kerb lines and drainage channels.

Information to document

• Layout: Plan showing bay positions, dimensions, aisle widths, entry and exit points and turning areas.
• Pavement construction: Thickness and materials of each layer, with compaction requirements.
• Levels and falls: Finished levels and gradients so that water drains to channels or gullies.
• Edge details: Kerb types and edge restraints around the parking area.
• Markings and accessories: Line markings, bay numbers, accessible bay symbols, wheel stops and signs.

3.1.1.2 Kerbs

Kerbs are edging units, usually precast concrete, laid along the edges of roads, parking areas, walkways and planting beds. They restrain the edges of the paving, guide surface water to drains, separate vehicles from pedestrians and give a neat finish. Kerbs are documented by type, size, profile and bedding, since these affect both cost and performance. Example: the internal road of a secondary school is documented with half-battered kerbs along the carriageway and flush kerbs where it meets the paved parade ground.

Information to document

• Type and profile: The kerb type and face shape required at each location.
• Dimensions: Width, height and unit length of the kerbs.
• Bedding and backing: Concrete bed and haunching thickness and grade.
• Straight and curved lengths: Positions and radii of curved kerbs at bends and junctions.
• Special units: Dropped kerbs, transition units and quadrants at corners.

3.1.1.3 Paving blocks

Paving blocks are precast concrete or clay units laid on a sand bed to form hard surfaces for walkways, courtyards, driveways and parking areas. They include plain rectangular blocks, concrete paving slabs and decorative blocks in different colours and textures. They are popular because they are durable, easy to repair by lifting and relaying individual blocks, and allow some water to pass through the joints. Example: the walkways and courtyard of a hotel are documented as 60 mm grey and red concrete paving blocks laid in a herringbone pattern on a 50 mm sand bed.

Information to document

• Block type and size: Material, shape, dimensions and thickness for each area.
• Colour and pattern: Colours and the laying pattern, such as stretcher bond or herringbone.
• Bedding and base: Sand bed thickness and base and sub-base layers.
• Edge restraint: Kerbs or edging that hold the blocks in place.
• Joint filling: Jointing sand and any sealing required.

3.1.1.4 Cabro

Cabro is the term widely used in Kenya for interlocking concrete paving blocks, which lock into each other by their shape, such as zigzag, I-shape or dog-bone profiles. The interlocking shape spreads vehicle loads across many blocks, so cabro paving is stronger and more stable than plain blocks of the same thickness and suits driveways, parking areas, petrol stations and estate roads. Cabro is laid on a compacted sand bed over a base course, vibrated into place, and the joints are filled with fine sand. Example: the estate road of a housing SACCO's development is documented as 80 mm zigzag cabro on a 50 mm sand bed over a 150 mm crushed stone base.

Information to document

• Shape and thickness: Interlocking profile and thickness for each area.
• Strength and colour: Concrete strength grade and colours or patterns.
• Pavement layers: Base, sub-base and bedding sand thickness and compaction.
• Falls and drainage: Levels and gradients leading to channels.
• Edge details and jointing: Edge restraints and joint sand.

3.1.1.5 Scope and Components of Landscaping Works

Landscaping includes a variety of components that must be individually measured and documented to reflect their quantities and specifications accurately.

• Earthworks and Ground Preparation: This involves clearing, grading, and leveling the site to prepare for planting or construction of landscape features. Measurement requires recording the volume of soil excavated, filled, or compacted.
• Planting and Vegetation: Includes grass, shrubs, trees, and flower beds. Quantities are measured by area (m²) for turf and flower beds, and by number for individual plants and trees.
• Hard Landscaping Features: Elements such as pathways, patios, retaining walls, and fences. These are measured by length, area, or volume depending on the feature.
• Irrigation Systems: Comprising pipes, sprinklers, and control units. Measurement is based on the length of piping and number of irrigation heads installed.
• Outdoor Furniture and Fixtures: Includes benches, lighting, and signage. These are quantified by number with specifications documented.

3.1.1.6 Measurement Principles for Soft Landscaping

Measurement of landscaping works requires adherence to principles that ensure accuracy and clarity.

• Use of Appropriate Units: Area measurements for planted zones, volume for earthworks, and counts for plants and fixtures.
• Inclusion of Preparation Works: Soil preparation and removal of debris must be included as separate items.
• Specification of Plant Sizes and Types: Different plant sizes and species have varying costs and maintenance requirements; these must be clearly documented.
• Measurement of Edges and Boundaries: Lengths of paths, borders, and fencing need precise linear measurement.
• Consideration of Seasonal Variations: Some landscaping elements might be seasonal; measurement should reflect actual quantities installed.

3.1.1.7 Documentation and Drawing References

Accurate documentation links measured quantities to design drawings and specifications.

• Use of Site Layout Plans: Landscaping areas are identified and dimensioned on site plans.
• Schedules of Planting: Detailed lists specifying species, sizes, and quantities.
• Specification Documents: Include materials, installation methods, and maintenance requirements.
• Photographic Records: For verification and quality control during execution.
• Coordination with Other Disciplines: Ensure landscaping does not conflict with drainage or utility works.

3.1.1.8 Challenges and Best Practices in Landscaping Documentation

Landscaping documentation can be complex due to site variability and natural materials.

• Irregular Site Boundaries: Use detailed site surveys to capture accurate dimensions.
• Variation in Plant Growth: Document initial sizes and condition to avoid disputes.
• Integration with Other Works: Coordinate with drainage and paving to avoid double counting.
• Use of Technology: Employ GIS and digital measuring tools for precision.
• Regular Site Inspections: Verify quantities and quality during installation.

3.1.2 Rendering works

Rendering involves applying a protective and decorative coating over external walls. It is a significant external finishing element that affects building aesthetics and weather resistance. In the Kenyan context, rendering is common in residential, commercial, and institutional buildings, requiring precise measurement for cost estimation and quality control.

Types and Materials of Rendering

Different rendering types require distinct measurement approaches.

• Cement and Sand Rendering: The most common, providing a durable finish. Measurement is by surface area (m²) applied.
• Lime Rendering: Used for heritage buildings, often requiring special handling.
• Acrylic and Polymer Renders: Modern synthetic materials offering flexibility and color options.
• Textured Renders: Include stippled or roughcast finishes, sometimes measured separately for surface texture.
• Scratch and Float Finishes: Different application techniques influencing thickness and coverage.

Measurement Techniques for Rendering

Rendering measurement must account for surface preparation and finishing layers.

• Measurement of Wall Surface Area: Calculated from architectural drawings, deducting openings such as windows and doors.
• Thickness and Layers: Where specified, thickness affects material quantities and labor.
• Surface Condition Allowance: Rough or uneven surfaces may require additional material.
• Measurement of Repairs and Patching: Separate items for patch repairs on existing surfaces.
• Inclusion of Surface Preparation: Cleaning, priming, or mesh installation must be measured separately.

Example: An external wall of a dispensary is 12 m long and 3 m high, with one window 1.5 m × 1.2 m and one door 0.9 m × 2.1 m.

Gross area = 12 × 3 = 36.00 m²

Openings = (1.5 × 1.2) + (0.9 × 2.1) = 1.80 + 1.89 = 3.69 m²

Net area = 36.00 − 3.69

Answer: 32.31 m² of rendering

Documentation and Specification Requirements

Proper documentation ensures the rendering works meet design and quality standards.

• Detailed Drawings: Elevations and sections indicating areas to be rendered.
• Material Specifications: Type, mix proportions, and curing requirements.
• Workmanship Standards: Guidelines for application methods and finishing.
• Quality Control Records: Test results for adhesion and durability.
• Health and Safety Plans: Handling of materials and site safety measures.

Practical Considerations and Quality Control

Rendering quality impacts building durability and appearance.

• Weather Conditions: Avoid application during heavy rain or extreme heat which can affect curing.
• Skilled Labor: Experienced plasterers ensure uniform thickness and finish.
• Curing Time: Adequate curing prevents cracking and delamination.
• Inspection and Testing: Regular site checks and adhesion tests maintain standards.
• Surface Protection: Post-application protection from damage during other external works.

3.1.3 Drainage works

Drainage is vital for managing surface and subsurface water around buildings, protecting foundations and landscaping. Drainage works also include the foul drainage that carries wastewater from the building to a sewer or to on-site treatment such as septic tanks, soak pits and biodigesters. Accurate measurement and proper documentation are essential for effective construction and maintenance, especially in Kenya’s varied climate zones.

3.1.3.1 Manholes

A manhole is an underground chamber large enough for a person to enter, built on a drain or sewer line to allow inspection, cleaning and repair. Manholes are placed at changes of direction, gradient or pipe size, at junctions and at regular intervals on long runs, and they are usually used where drains are deep. They are built of brick, block, precast concrete rings or in-situ concrete, with a benched channel at the base, step irons for access and a cover strong enough for the traffic above. Example: the foul drainage of a shopping mall is documented with manholes at each junction, showing invert levels, depths, internal sizes and heavy-duty covers in the parking area.

Information to document

• Location and numbering: Position of each manhole on the drainage layout, with a unique reference number.
• Levels: Cover level and invert levels of all incoming and outgoing pipes.
• Depth and internal size: Depth to invert and internal dimensions.
• Construction: Materials and thicknesses of base, walls and cover slab.
• Cover type: Duty rating of the cover and frame for the location.

3.1.3.2 Inspection chambers

An inspection chamber is a smaller, shallower access point on a drain that allows rodding and inspection from the surface without a person entering. It is used where drains are shallow, typically less than about 1 m deep, at bends, junctions and changes of gradient on domestic drainage. Inspection chambers are commonly built of brick or block or supplied as prefabricated plastic units. Example: the drainage for a private residence is documented with brick inspection chambers of 600 × 450 mm internal size at each bend and junction, with light-duty covers.

Manholes and inspection chambers compared

3.1.3.3 Soak pits

A soak pit is an underground pit, lined with open-jointed masonry or filled with stones, that allows wastewater to soak slowly into the surrounding soil. It commonly receives the liquid effluent from a septic tank or greywater from kitchens and showers, and works only where the soil is permeable and the water table is well below the pit. Soak pits must be located at safe distances from boreholes, wells and buildings to avoid contamination and damage. Example: a rural health centre with a septic tank is documented with a soak pit 2 m in diameter and 3 m deep, located well away from its water well.

Information to document

• Location and distances: Position relative to buildings, boundaries, wells and boreholes.
• Dimensions: Diameter or plan size and depth.
• Lining and fill: Lining type and any stone fill.
• Soil information: Percolation test results and water table level.
• Cover and inlet details: Cover slab, access opening and inlet pipe level.

3.1.3.4 Septic tanks

A septic tank is a watertight underground tank that receives sewage from a building, holds it long enough for solids to settle and partly break down, and discharges the clarified effluent to a soak pit or drainage field. It is used where there is no public sewer, and is normally divided into two chambers, the first about two thirds of the total volume, with baffles or tee pipes to stop scum and sludge leaving. The tank must be sized for the number of users, be accessible for desludging and be located at safe distances from buildings and water sources. Example: a boarding school without sewer connection is documented with a two-chamber septic tank sized for its population, with access covers for desludging and an outlet to soak pits.

A common sizing guide gives the capacity as C = 180P + 2,000 litres, where P is the number of users.

Example: Find the capacity of a septic tank for 20 users.

C = 180 × 20 + 2,000 = 3,600 + 2,000

Answer: 5,600 litres (5.6 m³)

3.1.3.5 Biodigester

A biodigester is an airtight tank in which organic waste, such as animal dung, toilet waste or food waste, is broken down by bacteria without oxygen to produce biogas and a nutrient-rich slurry. The biogas, mainly methane, is used for cooking, lighting or heating, while the slurry is used as fertiliser, and the system also treats waste that would otherwise pollute the environment. Biodigesters may be fixed-dome masonry, floating-drum or prefabricated plastic units, and they are increasingly used in place of septic tanks at institutions. Example: a dairy farm's biodigester takes cow dung from the zero-grazing unit and supplies biogas to the farmhouse kitchen, with the slurry spread on the fodder fields.

Information to document

• Type and capacity: Biodigester type and volume, linked to the daily waste input.
• Location: Position relative to the waste source, kitchen and buildings.
• Construction details: Materials, dimensions and waterproofing of each chamber.
• Gas system: Pipe sizes, routing, valves, water trap and appliances.
• Safety: Ventilation, gas leak precautions and fencing of openings.

3.1.3.6 Other Components of Drainage Systems

Drainage works comprise further elements beyond the chambers and treatment units above, and these must be documented distinctly.

• Surface Channels and Gutters: Collect and direct rainwater away from structures.
• Subsurface Drain Pipes: Perforated pipes that remove groundwater.
• Gullies and Catch Basins: Collect surface water and trap silt before it enters the drains.
• Drain Pipes: Carry foul and surface water between chambers, with sizes and gradients shown.
• Outlet Structures: Discharge water safely into natural or municipal systems.

3.1.3.7 Measurement Principles for Drainage Pipes and Channels

Drainage measurement involves linear, area, and volume quantities depending on the component.

• Linear Measurement of Pipes and Channels: Length recorded in meters along the centerline.
• Volume Measurement of Excavations: For trenches, based on cross-section and length.
• Bedding and Surround: Bedding and surround materials to pipes recorded separately.
• Pipe Sizes and Materials: Each pipe size and material described as a separate item.
• Material Quantities: Concrete, pipe materials, and bedding aggregates measured separately.

3.1.3.8 Documentation and Coordination

Drainage documentation must integrate with overall site plans and utility drawings.

• Drainage Layout Plans: Showing pipe routes, slopes, and connections.
• Specifications for Materials and Installation: Including pipe types and bedding requirements.
• Coordination with Other Services: Avoid conflicts with electrical conduits and landscaping.
• Maintenance Access Points: Clearly marked for future servicing.
• Inspection and Testing Records: Hydraulic performance and leak tests.

3.1.3.9 Challenges and Site Management in Drainage Works

Drainage installation faces practical challenges requiring careful management.

• Site Topography and Soil Conditions: Influence pipe routing and trench stability.
• Maintaining Correct Pipe Slopes: Essential for gravity flow; requires precise measurement.
• Protection Against Blockages: Use of filters and access points.
• Health and Safety Risks: Excavation hazards and waterborne disease risks.
• Environmental Compliance: Ensuring drainage does not cause erosion or pollution.

3.1.4 Procedure for documenting external works elements

1. Collect the drawings: Obtain site layout, landscaping, drainage and elevation drawings and the specifications.
2. Identify each element: List all external works elements, such as parking, kerbs, paving, cabro, rendering and drainage items.
3. Record descriptions: Write a full description of each element, including materials, sizes, thicknesses and finishes.
4. Reference locations: Link each element to its location and reference number on the drawings.
5. Note levels and falls: Record finished levels, invert levels and gradients for paving and drainage.
6. Check against specifications: Confirm that the descriptions agree with the specification and standards.
7. Clarify discrepancies: Raise queries with the designer on missing or conflicting information.
8. Compile and file: Organise the documentation by element so it can be used for quantification and booking.

Chapter Summary

This chapter covers the essential principles for applying construction external work taking off, beginning with detailed documentation of key external works elements. It explores landscaping works including vehicular parking, kerbs, paving blocks, and cabro, emphasizing their individual specifications and roles. Rendering works are addressed alongside vital drainage components such as manholes, inspection chambers, soak pits, septic tanks, and biodigesters, highlighting their structural and functional importance. The quantification of these external works elements follows, providing methods to accurately measure vehicular parking areas, kerbs, paving blocks, cabro, and various drainage installations. Finally, the chapter explains the systematic process of quantity booking for each element to ensure precise record-keeping and cost estimation. Together, these topics equip learners with a comprehensive understanding of how to document, quantify, and book external construction works effectively.